Separation systems for removing starch and other usable by-products from processing waste water

ABSTRACT

The present invention provides for a method for separating starch from processing solutions containing starch containing plants or roots such as potatoes, sweet potatoes, wheat, corn, tapioca, yams, cassaya, sago, rice, pea, broad bean, horse bean, sorghum, konjac, rye, buckwheat and barley to provide commercially acceptable starch while reducing disposal of solid or liquid waste matter into landfills or water treatment facilities.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under the provisions of 35 U.S.C. § 371 andclaims the priority of International Patent Application No.PCT/US2015/044794 filed on Aug. 12, 2015, which in turn claims priorityto U.S. Provisional Application No. 62/060,738 filed on Oct. 7, 2014,the contents of which are incorporated by reference herein for allpurposes.

BACKGROUND OF THE INVENTION Field of Invention

The present invention provides for a method for separating process waterby-products that consist of useable by-products, such as removing starchfrom processing solutions containing starch containing plants or rootssuch as from root plants such as potatoes, sweet potatoes, wheat, corn,tapioca, yams, cassaya, sago, rice, pea, broad bean, horse bean,sorghum, konjac, rye, buckwheat and barley while reducing disposal ofsolid or liquid waste matter into landfills or water treatmentfacilities.

Background of the Invention

In many food and dairy processing systems there is process watercontaining water, soluble organics and solid wastes. In the past, thisprocess water has been filtered and often chemically cleaned orbiologically degraded for disposal.

In most food processing facilities, there are process water by-productsthat consist of useable by-products, waste, soluble organic, and solidwastes. The process water typically includes an unacceptable level oforganic waste products measured in terms of it. Generally, the ChemicalOxygen Demand (COD) level in an organic process stream is directlyrelated to the carbon content in the process stream wherein the carboncontent in the process stream is usually in the form of starch and orsugar. When an organic stream is injected into wastewater, thedecomposition of the wastes depletes the oxygen supply in the waterbecause oxygen is needed to oxidize the waste in the water, and thus,making it difficult to support animal life. In addition the componentsin the fluid stream being measured in terms of COD, the components ofthe fluid and fluid stream may be expressed as Biological Oxygen Demand(BOD or Total Suspended Solids (TSS). Each may have different thresholdlevels for waste treatment facilities. BOD measures the quantity ofoxygen used in the aerobic stabilization of wastewater streams, is oneof the most widely used measure of general organic pollution inwastewater. Total solids in wastewater are defined as the residueremaining upon evaporation at just above the boiling point. The totalsolids are composed of matter which is settle able in suspension or insolution, and can be organic, inorganic, or a mixture of both.

Many Federal, State and local regulation place strict controls on thedischarge of process streams into the environment. As such, useableby-products should be separated from the process or waste streams inaddition to other by-products and wastes. In addition to compliance withregulations, it is beneficial to remove usable by-products or processstream components from the streams where the by-products can be used inthe manufacturing process thereby reducing cost or providing the sale ofby-products to other entities at a profit thereby increasing the totalrevenue for the manufacturing concern.

Starch is a carbohydrate found in many foods. It is a white andtasteless substance that can be processed to make numerous products,some of which are sugars, thickeners for foods such as corn starch,laundry starch, and adhesives. When certain root plants, such aspotatoes, sweet potatoes that include high starch content are sliced ordiced or chipped the physical action of cutting through the plant cellsreleases starch that is usually rinsed off with fresh water before goinginto the fryers or the next process. The starch is carried with the washdown water through the effluent system and commonly will go to drain.Alternatively there will be some kind of effluent treatment buteverything comes at a cost. The highest cost is no treatment at all inwhich case the producer will face high and ever increasing tradeeffluent charges based on the COD, BOD, and/or TSS levels in the wastethat is going down the sewer for the water companies to treat.

Many processors will want to find a solution for minimizing this addedCOD/BOS/TSS waste load on their treatment facility and recover thepotentially more valuable starch selling to other processersspecializing in starch refining, such as the use in the production ofanimal feed. Notably, there is also an opportunity to sell the starch ifit can be recovered because, for example, if potatoes are kept coldbefore slicing any starch released will have a value either as an animalfeed or for sale to companies that specialize in refining starch forfood, adhesives or other uses. Thus, it is important to find a way ofcapturing the starch before it ends up going down the drain.

Hydro-cyclones and/or centrifuge are commonly used for starch recoverybut these generally produce a wetter and more unmanageable starch. Plusthese systems typically do not efficiently recover a large amount of thestarch, allowing a significant portion of the total amount of starch inthe process water to remain suspended in the process water effluent fromthese treatments. Further, companies have to think about how theyinteract with the environment and reducing the pollution that goes downthe drain is an obvious benefit to all concerned. Implementing a new andnovel process that removes all or nearly all of the suspended starch ina process stream not only increases the total amount of starch recoveredfor sale or alternative use, it also provides a higher quality effluentof the process that may meet the manufacturers internal standards forprocess water inputs. Thus, there is also a possibility for reusing theclarified wash water which is certainly worth investigating.

In light of the above discussion, there is a need for separation systemsthat can be used continuously or non-continuously that can effectivelyseparate starch from process or waste water to provide dewatered starchproducts, thereby providing value added separated product and solid freestreams while producing a minimal amount of negative effects onwastewater treatment facilities.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a method toprocess starch removed from root plants such as potatoes or sweetpotatoes and other sources such as wheat, corn, tapioca, yams, cassaya,sago, rice, pea, broad bean, horse bean, sorghum, konjac, rye, buckwheatand barley by dewatering thereby providing separated water and aconcentrated viscous starch material.

In one aspect, the present invention provides for subjecting a processor waste water stream from processing of a starch containing source,wherein the process or waste water may be subjected to pretreatment toremove any unwanted solids, pulp, fibers, or debris by the use of screenmeshing, centrifugal filter, or a similar filtering device; and aseparation step wherein water is removed from the process or waste waterwith the use of a cross-flow filtration unit of the present invention toform a permeate water stream and a retentate starch stream.

A second purification step may be conducted on the permeate water streamto remove organic or inorganic products passed through the firstcross-flow filtration unit and which would constitute excess wastelevels for the local waste water treatment facility. For examplebiological oxygen demand (BOD) or total suspended solids (TSS) levelscan be reduced using a second cross-flow filtration unit that comprisesfiltration membranes having increased rejection characteristics orsmaller pore sizes, such as UF, NF, or RO membranes, than the firstcross flow filtration unit to provide essentially clear water permeatestream. The retentate starch, proteins and/or sugar containing stream ismoved on for further processing to produce desired commodities includingpurified starch, animal feed, adhesives, and other desirable separatedcomponents, such as, polyphenols, glycoalkaloids and nutritionalproducts.

In another aspect, the present invention provides for a separationmethod for separating water from starch containing liquid-type medium,the method comprising the steps of:

-   -   providing starch containing liquid-type medium, wherein the        liquid-type medium is a viscous liquid, non-viscous liquid, a        suspension or an emulsion;    -   providing at least one cross-flow filtration cassette        comprising:    -   an array of sheet members of generally rectangular and generally        planar shape with main top and bottom surfaces, wherein the        sheet members include in sequence in said array a first        retentate sheet, a first filter sheet, a permeate sheet, a        second filter sheet, and a second retentate sheet, wherein the        fatty acids and triglycerides, having a diameter larger than the        filter sheet's pore size, are retained in the retentate flow,        and at least a portion of the liquid medium with any permeate        species diffuse through the filter sheets and enter the permeate        sheet and permeate flow; and    -   directing the starch containing liquid-type medium through the        cross-flow cassette to separate starch from the liquid-type        medium.

Notably, the starch containing liquid-type medium may be pretreated toremove any unwanted material or larger solids from the liquid mediumbefore the separation process, wherein the pretreating may includesystems such as the cross-flow filtration cassette of the presentinvention, wherein the permeate and filter screens are sized forretention of the larger solids while allowing passage of starch contentinto a permeate stream, centrifuge, vibrating screen, mesh screening,belt filter, screw press, hydrocylcone and other systems that removedebris or further reduce particle size to ensure easy flow through thenext separation step.

Preferably, each of the sheet members in said array has at least oneinlet basin opening at one end thereof, and at least one outlet basinopening at an opposite end thereof, with permeate passage openings atlongitudinal side margin portions of the sheet members, wherein each ofthe first and second retentate sheets having a multiplicity of channelopenings therein, extending longitudinally between the inlet and outletbasin openings of the sheets in the array, and being bonded to anadjacent filter sheet about peripheral end and side portions thereof,with their basin openings and permeate passage openings in register withone another and the permeate passage openings of each of the retentatesheets being circumscribingly bonded to the adjacent filter sheet, andwith a central portion of each of the retentate sheets and adjacentfilter sheets being unbonded to permit permeate contacting the retentatesheet to flow through the filter sheet to the permeate sheet.

In yet a further aspect, the present invention provides for a system toprocess starch milk having a dry matter content of about 1% to about60%, preferably from about 35% to about 40%, wherein the starch milk isdewatered using the system of the present invention and recuperating adewatered starch with a water content of less than 50% residualmoisture, and more preferably less than about 20% residual moisture.

Additionally, the starch content can be as low as about is 1-20% in thestarch milk, and thus, there is no need for pretreatment such as use ofa centrifuge or hydrocylcone. Additional drying may be necessary so thatthe end product meets the standards of the commercial product, as itneeds dewatering of up to 20% of moisture. Importantly the dewateringstep is conducted without using high temperatures, that being preferablynot higher than about 35° C., in order to avoid gelatinization whichdestructs the granular structure of starch.

In a still further aspect, the present invention provides for a systemto separate starch milk from starch containing sludge, wherein thestarch containing sludge includes secondary products such as pulp andfruit water. Pulp is a major by-product that is part of sludge whetherdue to cutting or rasping of a starch containing plant or root andlikely includes some free starch that can be removed by additionalpasses through the cross filtration cassettes of the present invention.Further dewatering of the pulp can be enhanced by adding Ca(OH)₂ to thepulp which has the ability to change the structure of pectins so thatthe pulp does not retain as much water and the dewatering is moreeffective. The end result of dewatered pulp can be used as foralternative uses such as cattle feed and other agricultural orindustrial products. Additional starch can be released by processing thepulp through additional cutting or grinding steps, thereby releasingstarch granules that would otherwise remain in the pulp and enabling theuser to gain additional starch recovery and related revenues withoutdiminishing the value of the pulp as cattle feed or other uses.

Tubers or root starch containing plants also include water solubleproducts that are transferred to a water stream used in preparation ofproducts from such tuber or root starch containing plants. The fruitwater can be used in irrigation practice but it can also be used as amedium for protein production for yeast and thus has additional value.

In yet another aspect, the present invention provides for production offood quality starch from potato starch containing sludge, wherein thepotato starch containing sludge comprises starch milk includinghydrolyzed and/or non-hydrolyzed starch, process or waste water, potatopulp or fibers and fruit juice, the method comprising:

a) moving the potato starch containing sludge through a first cross-flowfiltration unit according to the present invention wherein such potatostarch containing sludge is separated and the starch milk, waste water,and fruit juice is separated into a permeate stream and the remainingpotato pulp and fibers are collected for further use;b) moving the permeate stream through a second cross-flow filtrationunit according to the present invention wherein the permeate compriseswaste water and fruit juice and the retentate stream includes starchmilk;c) moving the starch milk through a third cross-flow filtration unitaccording to the present invention, wherein the starch milk isconcentrated and dewatered and wherein the removed water is directedinto the permeate stream and the starch in the retentate stream iscollected, wherein the starch content is at least 20% and morepreferably from about 30% to 60%; andoptionally combining the waste water and fruit juice from step b) andthe water from step c) and moving into a fourth cross-flow filtrationunit according to the present invention wherein the fruit juice isremoved from the water thereby providing for a cleaned water stream thatcan be reused and the fruit juice that has been retained in theretentate stream can be collected for further use.

Other aspects and advantages of the invention will be more fullyapparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the components of a cross-flow filtration cassette used inthe separation of starch.

FIG. 2 shows the flow pattern of the retentate through a multiplicity ofsheets adapted to end plates with retentate inlet and outlet andpermeate inlet and outlet.

FIG. 3 shows a system for dewatering a tank of collected starch milk.

FIG. 4 shows the separation of purified starch from potato starchcontaining sludge.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a system for treating of a starch containingsolution for the separation of starch from the liquid solution.

The term “starch” refers to starches are obtained from seeds, tubers, orroots of different plants. Starch occurs in the form of tiny whitegranules at various sites in the plants. The diameter of the granulesvaries from one to 150 μm depending on the source. The term includesboth hydrolyzed and non-hydrolyzed starch.

The term “cross-flow filtration cassette” refers to a type of filtermodule or filter cassette that comprises a porous filter element acrossa surface of which the liquid medium to be filtered is flowed in atangential flow fashion, for permeation through the filter element ofselected component(s) of the liquid medium. In a cross-flow filter, theshear force exerted on the filter element (separation membrane surface)by the flow of the liquid medium serves to oppose accumulation of solidson the surface of the filter element. Cross-flow filters includemicrofiltration, ultrafiltration, screens and nanofiltration systems.The cross-flow filter may comprise a multiplicity of filter sheets(filtration membranes) in an operative stacked arrangement, e.g.,wherein filter sheets alternate with permeate and retentate sheets, andas a liquid to be filtered flows across the filter sheets, impermeatespecies, e.g. solids or high-molecular-weight species of diameter largerthan the filter sheet's pore size, are retained and enter the retentateflow, and the liquid along with any permeate species diffuse through thefilter sheet and enter the permeate flow. In the practice of the presentinvention, cross-flow filtration is a preferred separation method.Cross-flow filter modules and cross-flow filter cassettes useful forsuch filtration are commercially available from Smartflow Technologies,Inc. (Apex, N.C.). Suitable cross-flow filter modules and cassettes ofsuch types are variously described in the following United Statespatents: U.S. Pat. No. 4,867,876; U.S. Pat. No. 4,882,050; U.S. Pat. No.5,034,124; U.S. Pat. No. 5,034,124; U.S. Pat. No. 5,049,268; U.S. Pat.No. 5,232,589; U.S. Pat. No. 5,342,517; U.S. Pat. No. 5,593,580; andU.S. Pat. No. 5,868,930; the disclosures of all of which are herebyincorporated herein by reference in their respective entireties.

In one particular aspect, the present invention relates to a cross-flowfiltration cassette, as shown in FIG. 1, comprising a multilaminatearray of sheet members of generally rectangular and generally planarshape with main top and bottom surfaces, wherein the sheet membersinclude in sequence in said array a first retentate sheet, a firstfilter sheet, a permeate sheet, a second filter sheet, and a secondretentate sheet, wherein each of the permeate and filter sheet membersin said array has at least one inlet basin opening 10 at one endthereof, and at least one outlet basin opening 12 at an opposite endthereof, with permeate passage openings 13 at longitudinal side marginportions of the sheet members;

a. each of the first and second retentate sheets having at least onechannel opening 8 therein, extending longitudinally between the inlet 10and outlet basin 12 openings of the permeate and filter sheets in thearray, and being compression bonded to an adjacent filter sheet aboutperipheral end and side portions thereof, with their basin openings andpermeate passage openings in register with one another and the permeatepassage openings of each of the retentate sheets being circumscribinglycompression bonded to the adjacent filter sheet, and with a centralportion of each of the retentate sheets and adjacent filter sheets beingunbonded to permit permeate contacting the retentate sheet to flowthrough the filter sheet to the permeate sheet; andb. each of the filter sheets being secured at its peripheral portions ona face thereof opposite the retentate sheet, to the permeate sheet.

The term “sheet” will denote the generally planar members of thecassette, the cassette thus comprising an assembly of permeate sheets,filter sheets, and retentate sheets, coupled to one another in suchmanner as to permit flow of the fluid to be separated through the flowchannel(s) of the device, for mass transfer involving passage of thepermeate through the filter sheets, and retention of the retentate onthe side of the filter sheet opposite the side from which the permeateemerges.

The term “compressible” in reference to the retentate sheet or otherstructural feature or sheet member of the present invention means thatsuch component or member is compressively deformable by application ofload or pressure thereon.

The above-described filtration cassette of the invention comprises a“base sequence” of elements, defined as a sequence of sheet elementsconstituting a compressible retentate sheet (hereafter designated by thesymbol “CR”), a filter sheet (hereafter designated by the symbol “F”), aforaminous permeate sheet (hereafter designated by the symbol “P”), asecond filter sheet (“F”), and a second compressible retentate sheet(“CR”), thereby providing a sequence of sheet elements, CR/F/P/F/CR.

The base sequence of sheet elements may be utilized in construction offilters comprising a plurality of filtration cassettes, wherein thecompressible retentate sheet is utilized to seal the top and bottomelements of a plurality of filtration cassettes of a sequence,comprising compressible retentate sheet “CR”, filter sheet “F”,foraminous permeate sheet P, filter sheet “F”, non-compressibleretentate sheet “R”, filter sheet “F”, foraminous permeate sheet P,filter sheet “F”, and compressible retentate sheet “CR”. An illustrativestacked cassette filter according to the invention may for examplefeature the sheet sequence CR/F/P/F/R/F/P/F/R/F/P/F/CR as shown in FIG.2, comprising a first compressible retentate sheet, two base sequencesof sheets FPFRFPF in a repetitive sequence, and a second compressibleretentate sheet. In all repetitive sequences, other than a singlecassette base sequence, the following relationship is observed: where Xis the number of filter sheets F, the quantity 0.5 X-1 is the number ofnon-compressible retentate sheets R, and the quantity 0.5 X is thenumber of foraminous permeate sheets P, with two compressible retentatesheets being utilized to seal the top and bottom extremities of theintervening sequence. The cassettes may also be used in series orparallel.

Thus, it is possible to utilize a large number of base sequencecassettes in a repetitive sequence, to provide a stacked cassette filterof the desired mass transfer area. Many configurations are possible. Itis feasible in some instances, e.g., for mass transfer studies andsystem quantitation, to utilize a single cassette comprising the basesequence CR/F/P/F/CR wherein the outermost retentate sheets in thesequence are compression-sealed at their outer faces to an end plateaccommodating removal of permeate from the permeate passage openings ofthe constituent sheet members in the cassette.

The sheets of filter material used in the cassette article of thepresent invention may be of any suitable porosity rating. As usedherein, the porosity rating of a sheet of filter material is thesmallest particle size which cannot pass through the pores of the filtermaterial. Typical porosity ratings are expressed in molecular weight(MW), a salt rejection rate, or micrometer units, e.g., a 2 micronfilter media sheet being a material which will pass particles smallerthan 2 microns in diameter through the pores of the material, whileparticles larger than 2 microns will not be passed through the filtermaterial, and a salt rejection rate of 99% will retain 99% of a givensalt or small molecular with compound (MgSO4, for example) and allowwater or smaller molecules to pass through at a given set of conditionsof pressure, crossflow rate and temperature, and as a further example, a10,000 MW filter media sheet being a material which will pass particlessmaller than 10,000 MW in diameter through the pores of the material,while particles larger than 10,000 MW will not be passed through thefilter material.

In one preferred embodiment of the cassette article of the presentinvention, a retentate sheet is provided with a plurality oftransversely spaced-apart, longitudinally extending ribs or partitions,extending upwardly from (the central portion of) each of the main topand bottom faces of the retentate sheet, such ribs or partitions beingof substantially the same height and substantially parallel to oneanother to define a series of channels between the partitions, extendinglongitudinally between the respective basin openings of the retentatesheet, on both faces thereof. The adjacent filter sheets may be furtherbonded to the outer extremities of the ribs or partitions, and the ribsor partitions may be formed of any suitable material, e.g., a flexibleresilient adhesive bonding medium, such as a urethanes, epoxy orsilicone adhesive sealant medium, e.g., applied in a “bead” in thelongitudinal direction of the retentate sheet on both main top andbottom faces thereof.

The term “bonded” in reference to adjacent sheets in the multilaminatecassette means that the adjacent sheets are secured to one another insuch manner as to prevent flow of the material being processed, e.g.,the feed material to be separated, as well as component materialstherefrom (filtrate or permeate, as well as retentate), from flowingthrough such secured areas or between the adjacent sheets at suchsecured areas. Preferably, the bonding is carried out by compressivebonding or with a suitable adhesive or sealant medium, e.g., a urethane,epoxy, cyanoacrylate, or silicone adhesive material, which fills theinterstices of the foraminous sheet in the bonded pair of sheets, andadhesively joins one of the adjacent sheets to the other in the bondedareas.

The term “compressive bonding” and “compressively bonded” refer tobonding and bonding operations in which the structure being bonded issubjected to a compressive load or force, for sufficient time and undersufficient period to effect the bonding securement of the structure.Compressive bonding of laminae in the practice of the invention ishighly desirable, in order to assure the leak-tightness and structuralintegrity of the resulting multilaminate assembly of the cassette.

The invention may for example be carried out with bonding of sheets inthe multilaminate array to one another with cyanoacrylate or other“fast” adhesives, or alternatively the adhesive or sealant medium mayrequire extended cure at ambient temperature or other appropriate cureconditions, and it may be advantageous to conduct such cure with thelaminate structure in a fixture or other assembly in which thecompressive bonding is effectively completed.

In a specific aspect of the invention, each of the foraminous permeatesheets may constitute a foraminous material of from about 80 to about300 mesh size. Each of the foraminous permeate sheets may for examplecomprise a woven polymeric mesh, e.g., of a material selected from thegroup consisting of polyester, polypropylene, nylon, fluorocarbonpolymers such as polytetrafluoroethylene, polyethylene, and polysulfone,and composites comprising one or more of such materials.

The filter sheets used in the filtration cassette of the presentinvention may be of any suitable materials, such as a material selectedfrom the group consisting of cellulose, polyphenylene oxide,polysulfone, cellulose nitrate, cellulose acetate, regeneratedcellulose, polyether amide, polyphenylene oxide/polysulfone blends,mixed esters of cellulose, and polyether sulfone.

Furthermore, it is possible to optimize the separate processes withcross-flow filtration modules of variable channel velocities but ofuniform channel heights, given the fact that most commercial cross-flowmodules are only available in a single channel height. When the channelheight of a cross-flow filtration module is known, shear is directlyproportional to channel velocity of such module for the same solutionpassing by.

In the literature, numerous techniques have been proposed to effect theseparation of target substances using membrane separations with additionof foreign substances such as acid, base, salt and solvents. In contrastto these chemical additives-based methods, the methodology of thepresent invention permits a target substance to be separated from aninput fluid by the simplest mechanical means. In the use of cross-flowfiltration modules of the type described in the aforementioned patents,the specificity and speed of a desired separation is effected by a)fluid distribution in the cross-flow module, b) channel height of thecross flow module, c) channel length, d) shear rate, e) membrane porestructure, f) membrane structure, g) membrane chemistry, h)trans-membrane pressure, and i) pressure drop, which is a function ofchannel length, velocity and solution viscosity.

The approaches by others involving various additives and manipulationsof transmembrane pressure appear to be predicated on overcoming problemscreated by poor distribution of flow within the cross-flow module. It isnot to say that the addition of salts and solvents do not have a placein separation but without proper flow distribution the membraneseparation cannot be optimally operated nor will cleaning techniques befully beneficial. It will be appreciated, based on the disclosure hereinthat numerous heretofore expensive or difficult separations are renderedfar simpler and more economical by employing the techniques describedherein.

Thus, the invention relates in another aspect to optimizing the membraneseparation process, comprising:

a. selecting a cross-flow membrane module wherein the distance from theinlet port to the outlet port is equidistant from the inlet to outletfor each sub-channel of the device, i.e., each sub-channel is of a samedimensional character;

b. selecting an optimal channel height;

c. selecting an optimal shear rate and/or channel velocity;

d. selecting an optimal transmembrane pressure;

e. selecting an optimal rejection characteristics of the filtermembrane;

f. selecting an optimal temperature;

g. selecting an optimal channel length; and

h. selecting an optimal pressure drop which is the composite of

i. the optimal channel height;

j. the optimal shear rate and/or channel velocity;

k. optimal channel length; and

l. the viscosity of the solution being filtered.

Selecting a channel height can be performed mathematically orempirically by trial and error noting that the starch solution isfrequently non-Newtowian. The objective of channel selection is tominimize channel height with three critical stipulations: first, thechannel must be sufficiently high to allow the unrestricted passage ofany larger material such as clumped cells; second, the channel shouldnot cause excessive pressure drop and loss of linear efficiency; andthird, the channel should be sufficiently high as to allow the properangle of attack for substances to encounter the membrane pore and passthrough the pore. The optimal channel height is dependent on the lengthand viscosity of the solution.

Several notable observations have been made in initial trials andprocess scale-up, as discussed below.

For suspensions having an optical density (OD) of 2 to 500, and a pathlength of 6 to 12 inches, start with a channel height between 0.4 to0.75 mm. If the inlet pressure is above 15 PSIG at a velocity of 2.0M/sec, then the channel is too thin.

For suspensions having an optical density (OD) of 2 to 500, and a pathlength of 6 to 12 inches, start with a channel height between 0.4 to0.75 mm. If the inlet pressure is below 5 PSIG at a velocity of 2.0M/sec the channel is too high.

For suspensions having an optical density (OD) of 2 to 500, and a pathlength of 25 to 40 inches, start with a channel height between 0.7 to1.0 mm. If the inlet pressure is above 15 PSIG at a velocity of 2.0M/sec, the channel is too thin.

For suspensions having an optical density (OD) of 2 to 500, and a pathlength of 25 to 40 inches, start with a channel height between 0.7 to1.0 mm. If the inlet pressure is below 5 PSIG at a velocity of 2.0M/sec, the channel is too high.

Another aspect of the present invention relates to a stacked cassettecross-flow filter comprising cassette articles of the type describedabove.

Still another aspect of the present invention relates to a pair of endplates or manifold assembly in which the cassettes are secured foroperation as shown in FIG. 2.

FIG. 3 shows a system for dewatering a tank 14 of collected starch milk.The starch milk is removed from the tank and is introduced to thecross-flow filtration cassette 18 wherein the starch milk is separatedinto a retentate and a permeate stream. The retentate stream comprisingthe dewatered starch may be returned to the tank via process line 22 forfurther dewatering or sent on for further processing (not shown). Thepermeate (separated water) is introduced to the permeate vessel 20.Notably, the permeate can be further filtered using a second cross-flowfiltration cassette of the present invention to further removeimpurities and provide purified water that can be imported into awastewater stream.

The components of the cross-flow filtration cassette 18 are described inFIG. 1 and relates to a filtration cassette comprising a multilaminatearray of sheet members of generally rectangular and generally planarshape with main top and bottom surfaces, wherein the sheet membersinclude:

a. a first compressible retentate sheet of suitable material, e.g.polysulfone, polyethersulfone, polycarbonate, urethane, silicone, orother compressible material of construction, having (i) at least onelongitudinally extending rib or partition element 6, such partitionelement(s) when provided in multiple configuration being transverselyspaced apart from one another and being of substantially the same heightand substantially parallel to one another to define a single or a seriesof channels 8 between the partitions, extending longitudinally betweenthe respective inlet 10 and outlet 12 basin openings of associatedfilter elements and permeate sheet members, on both faces thereof, (ii)permeate passage openings 13 at side portions of the sheets, and (iii)the retentate sheet aligned to the first sheet of filter material atrespective end and side portions thereof, with the basin openings andpermeate passage openings of the associated sheet members in registerwith one another and the permeate passage opening of the retentate sheetmember being circumscribingly compressed to the first sheet of filtermaterial, and with a central portion of the first sheet of filtermaterial and the retentate sheet member being unbonded to permitpermeate contacting the retentate sheet member to flow through the firstsheet member of filter material to the foraminous permeate sheet member;b. a first sheet member of filter material having (i) multiple basinopenings, of a suitable shape, e.g., polygonal, semicircular, or sectorshape, at each of opposite end portions of the sheet member definingrespective inlet 10 and outlet 12 passages, each basin being bounded bygenerally linear side edges defining corners of the basin at respectiveintersections of the side edges, and (ii) permeate passage openings 13at the side portions of the sheet member, wherein the first sheet memberof filter material is bonded to the foraminous permeate sheet member attheir respective end and side portions, with their basin openings andpermeate passage openings in register with one another and the basinopenings being circumscribingly bonded at respective end portions of thefirst sheet member of filter material and the foraminous permeate sheetmember, and with a central portion of the first sheet member of filtermaterial and the foraminous permeate sheet member being unbonded so asto define a central portion permeate channel of the foraminous permeatesheet communicating with the permeate passages in the first sheet memberof filter material and in the foraminous permeate sheet member;c. a foraminous permeate sheet member of screen or mesh material, having(i) multiple basin openings of suitable shape at each of opposite endportions of the sheet member defining respective inlet 10 and outlet 12passages, each basin being bounded by generally linear side edgesdefining corners of the basin at respective intersections of the sideedges, and (ii) permeate passage openings 13 at the side portions of thesheet member;d. a second sheet member of filter material having (i) multiple basinopenings at each of opposite end portions of the sheet member definingrespective inlet 10 and outlet 12 passages, each basin being bounded bygenerally linear side edges defining corners of the basin at respectiveintersections of the side edges, and (ii) permeate passage openings 13at the side portions of the sheet member, wherein the second sheetmember of filter material is compression sealed to the retentate sheetmember at their respective end and side portions, with their basinopenings and permeate passage openings in register with one another andthe permeate passage opening of the retentate sheet member beingcompression sealed to the second sheet member of filter material, andwith a central portion of the second sheet member of filter material andthe retentate sheet member being unbonded to permit permeate contactingthe retentate sheet member to flow through the second sheet member offilter material; ande. a second compressible retentate sheet member of suitable material,e.g. polysulfone, polyethersulfone, polycarbonate, urethane, silicone,having (i) at least one longitudinally extending rib or partitionelement 6, provided that when multiple partition elements are employed,the partition elements are transversely spaced-apart from one another,such partition elements being of substantially the same height andsubstantially parallel to one another, to define a single channel 8 or aseries of channels between the partitions, extending longitudinallybetween the respective inlet and outlet basin openings of the filterelements and permeate sheet members, on both faces thereof, (ii)permeate passage openings 13 at the side portions of the sheet member,and (iii) the retentate sheet compression sealed to the second sheet offilter material at respective end and side portions thereof, with theirbasin openings and permeate passage openings in register with oneanother and the permeate passage opening of the retentate sheet memberbeing compression sealed to the second sheet member of filter material,and with a central portion of the first sheet member of filter materialand the retentate sheet member being unbonded to permit permeatecontacting the retentate sheet member to flow through the second sheetmember of filter material to the foraminous permeate sheet member.

In operation, the cross-flow filtration cassette provides a barrierthrough which the starch is substantially restricted from passingthrough the filter sheets and allows the starch concentration to beincreased.

After passing through the cross-flow filtration cassette, the permeatepreferably includes a greatly reduced amount of starch. The retentate,which is returned to tank and cassette may still include some water andthus can be recirculated again. The water permeate may be furtherpurified with the use of a second cross-flow filtration cassette whereinthe pores of the filter sheet comprises a smaller diameter than theoriginally used cassette.

FIG. 4 shows the starch process and illustrates one embodiment forseparating purified starch from potato starch containing sludge.Initially, the potato starch containing sludge, comprising starchpulp/fibers, starch milk, fruit juice, water and process or waste wateris first treated to remove large pulp and fibers that are retained inthe retentate stream for further treatment or use as an animal feed. Thepermeate stream is moved on to another cross-flow filtration cassette ofthe present invention wherein the process or waste water and fruitjuices are separated from the starch milk and the remaining retentateincludes the purified and concentrated starch product.

That which is claimed is:
 1. A method for production of food qualitystarch from potato starch-containing sludge, wherein the potatostarch-containing sludge comprises starch milk, waste water, potato pulpor fibers, and fruit juice, wherein the starch milk comprises hydrolyzedstarch and non-hydrolyzed starch, the method comprising: a) moving thepotato starch-containing sludge through a first cross-flow filtrationunit, wherein the potato starch-containing sludge is separated into afirst permeate stream comprising the starch milk, waste water, and fruitjuice, and a first retentate stream comprising the remaining potato pulpor fibers; b) moving the first permeate stream through a secondcross-flow filtration unit, wherein the first permeate stream isseparated into a second permeate stream comprising waste water and fruitjuice and a second retentate stream comprising starch milk; c) movingthe second retentate stream through a third cross-flow filtration unit,wherein the second retentate stream is separated into a third permeatestream comprising water and a third retentate stream comprisingdewatered starch; and d) combining the second permeate stream and thethird permeate stream and moving same into a fourth cross-flowfiltration unit to separate the water from the fruit juice, wherein saidwater is in a fourth permeate stream and said fruit juice is retained ina fourth retentate stream, wherein the third retentate stream comprisesat least 20% dewatered starch, wherein a temperature of step (c) is nothigher than about 35° C. to avoid the destruction of a granularstructure of the dewatered starch.
 2. The method of claim 1, wherein thecross-flow filtration unit comprises: an array of sheet members ofgenerally rectangular and generally planar shape with main top andbottom surfaces, wherein the sheet members include in sequence in saidarray a first retentate sheet, a first filter sheet, a permeate sheet, asecond filter sheet, and a second retentate sheet, wherein the first andsecond filter sheets comprise pores having a known size, wherein solidsor high-molecular weight species having a diameter larger than the sizeof the pores of the first and second filter sheets, can be retained in aretentate stream, and any liquid or permeate species can diffuse throughthe first and second filter sheets and enter the permeate sheet and apermeate stream.
 3. The method of claim 2, wherein each of the sheetmembers in said array has at least one inlet basin opening at one endthereof, and at least one outlet basin opening at an opposite endthereof, with permeate passage openings at longitudinal side marginportions of the sheet members, wherein each of the first and secondretentate sheets have a multiplicity of channel openings, extendinglongitudinally between their inlet and outlet basin openings, and saidretentate sheets are bonded to an adjacent filter sheet about peripheralend and side portions thereof, wherein their inlet basin openings,outlet basin openings, and permeate passage openings are in registerwith one another and the permeate passage openings of each of theretentate sheets are circumscribingly bonded to the adjacent filtersheet, wherein liquid and permeate species contacting the filter sheetin the channel openings of the retentate sheets flow through the filtersheet to the permeate sheet.
 4. The method of claim 1, wherein the fruitjuice comprises sugars, macromolecules, and salts.
 5. The method ofclaim 1, wherein the third retentate stream comprises from about 30% to60% dewatered starch.
 6. The method of claim 1, wherein the firstretentate stream comprising the remaining potato pulp or fibers streamis recovered for use as an animal feed or for further treatment.